The present invention relates to hydraulic control valves, in particular, for the manual control of hydraulic power machines such as double acting cylinders, reversible hydraulic motors and the like. The invention being particularly aimed at providing a single control valve which will enable the operation of more than one such hydraulic machine alternately or multiples of said hydraulic machinery selectably at a similar time. The invention will hereinafter be described in relation to the control valve being adapted to control hydraulic lift cylinders, however, it will be readily apparent that the invention is also applicable to controlling any other hydraulically powered machine.
Conventionally, hydraulic speed and directional control valves have been designed as singular operative units such that they control one hydraulic cylinder, or simultaneously additional hydraulic cylinders. Such control valves have generally been not capable of selectively operating separate hydraulic cylinders, or selectably one or more but not all of the hydraulic cylinders simultaneously.
To overcome this shortcoming, several means have been used in the prior art. These include "stacking" of valves or by using cross-over linkages, and/or specific operator levers and linkage connections. When used in multiple connections there are several disagreeable factors involved such as, excessive horsepower needed for operation, extreme linkage wear, and poor control over two or more lift cylinder operations. Such arrangements may suffer from difficulties in controlling the amount of oil distributed into the separate lift cylinders thus adversely affecting the speed at which the hydraulic lift cylinders operate in a loaded or unloaded movement, moreover the cost of supplying and installing these conventional type arrangements can be quite high and they require significant space for correct installation on machinery where such space is often difficult to find. The arrangement can themselves be quite heavy which is not an advantage. In addition such arrangements can cause restrictions in the flow of hydraulic fluid and as a result they may cause overheating with consequent poor efficiency of operation. It is therefore considered desirable from a number of factors to be able to replace these existing complex valve and linkage arrangements with a single control valve which is simple to operate and which enables the desired control of hydraulic lift cylinders or the like connected thereto.